Aura Diagnostics Reference

Single source of truth for every diagnostic the Aura toolchain can report. aura/transpiler/errors.py mirrors this document; a test (tests/test_diagnostics.py) asserts the two stay in sync.

A diagnostic is either an error (prefix E, stops compilation / fails the command) or a warning (prefix W, reported but non-fatal).

Format

<file>:<line>:<column>: <severity> [<code>]
  <message>
  hint: <how to fix it>

The file:line:column prefix is omitted only when no location is known (for example, a whole-program rule). Every checker attaches a real SourceLocation.

Numbering

Range	Area
E0xx	Lexical and syntax errors
E1xx	Type errors
E3xx	Semantic / structural errors
E4xx	I/O, configuration, environment
E9xx	Fatal / internal
W0xx	Style and formatting warnings
W1xx	Unused / redundant-code warnings
W2xx	Semantic warnings

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Errors — lexical and syntax (E0xx)

Code	Name	Message	Emitted by
E004	INVALID_SYNTAX	Construct is not allowed here	rule checker

The parser reports lexical and syntax errors by raising a structured SyntaxError that carries line/column/filename. These are surfaced directly by the CLI and the LSP rather than as a separate code. E004 is emitted by the rule checker for constructs the parser accepts but the language rules reject.

Errors — types (E1xx)

Code	Name	Message	Emitted by
E101	TYPE_MISMATCH	expected <T>, got <U>	type checker
E105	WRONG_ARGUMENT_COUNT	function called with the wrong arity	type checker
E106	WRONG_ARGUMENT_TYPE	argument of the wrong type	type checker
E108	INCOMPATIBLE_OPERANDS	operator used on incompatible operands	type checker
E109	NON_EXHAUSTIVE_MATCH	'match' over <subject> is not exhaustive	type checker (warning; see note)
E110	UNKNOWN_TYPE_CONSTRAINT	type parameter '<name>' has unknown constraint '<constraint>'	type checker

Note on E109: NON_EXHAUSTIVE_MATCH carries an E prefix but is emitted as a warning (_add_warning), not an error. This is intentional: a non-exhaustive match is a correctness risk, but blocking compilation would break existing code that relies on wildcard fallthrough. The W prefix is reserved for style and unused-code warnings; E109 occupies the E1xx range because it is a type-system diagnostic.

Undefined-name and non-callable diagnostics are not emitted: Aura is gradually typed and resolves names at runtime, so a name the checker cannot prove is left to Python rather than reported. See “Removed codes” below.

Errors — semantic / structural (E3xx)

Code	Name	Message	Emitted by
E301	DUPLICATE_DEFINITION	name already defined in this scope	rule checker
E302	UNREACHABLE_CODE	statement is unreachable	rule checker
E303	REASSIGN_IMMUTABLE	reassigning a let/const binding, a class const member, or module state from outside	mutability checker, rule checker
E307	MISSING_VISIBILITY	class/trait member has no visibility	rule checker
E308	INACCESSIBLE_MEMBER	non-public class member or non-exported module member accessed from outside	rule checker
E309	UNIMPLEMENTED_ABSTRACT	concrete class missing an abstract method	rule checker
E310	MISSING_MAIN	entry file has no main	rule checker
E311	INVALID_MAIN	main has a bad signature	rule checker
E312	MAIN_IN_MODULE	main declared inside a module body (never runs)	rule checker
E313	UNRESOLVED_REEXPORT	a module re-exports a name no sibling source defines	rule checker
E314	UNKNOWN_BASE_CLASS	extends names a base that does not exist	rule checker
E315	INVALID_INHERITANCE	duplicate base or circular inheritance	rule checker
E316	INSTANTIATE_ABSTRACT	instantiating a trait, an abstract class, or a class with unimplemented abstract methods	rule checker
E317	SELF_IN_STATIC	self/cls used in a static method	rule checker
E318	UNKNOWN_LABEL	break/continue names a label that is not an enclosing loop	rule checker
E319	USED_BEFORE_DECLARED	a local is used before its declaration	mutability checker
E320	DECORATOR_ON_FIELD	a method decorator applied to a field	reserved (parser raises SyntaxError directly)
E321	ABSTRACT_SUPER_CALL	super.method() targets an abstract method with no implementation	rule checker

Note on E320: DECORATOR_ON_FIELD is defined in the enum for forward compatibility but is not yet wired up. The parser raises SyntaxError directly when a decorator appears on a field. When the rule checker is extended to emit structured diagnostics, E320 will be used.

Errors — I/O and configuration (E4xx)

There is no code in this range. I/O and configuration failures (a missing file, an unreadable path, a bad project layout) are reported by the CLI as a plain message with a non-zero exit status, not as a numbered diagnostic.

Errors — fatal (E9xx)

Code	Name	Message	Emitted by
E999	FATAL	too many errors; compilation stopped	error collector

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Warnings — style (W0xx)

Produced by aura lint. Non-zero exit unless --allow-warnings is passed.

Code	Name	Message	Emitted by
W001	LINE_TOO_LONG	line exceeds the recommended width	linter
W002	TRAILING_WHITESPACE	line has trailing whitespace	linter
W003	NAMING_CONVENTION	identifier is not snake_case / PascalCase	linter
W004	SPACING	multiple spaces after a keyword	linter

Warnings — unused / redundant (W1xx)

Code	Name	Message	Emitted by
W103	UNUSED_TYPE_PARAMETER	generic type parameter is never used	type checker

Unused-variable and unused-import warnings are not emitted; see “Removed codes” below.

Warnings — semantic (W2xx)

Reserved for future semantic warnings; none are emitted today.

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Removed codes

These were defined historically but never emitted; they are removed to keep the catalogue honest.

Code	Reason
E201–E204	runtime faults are surfaced as native Python exceptions; no Aura diagnostic is emitted
E401, E402	I/O and configuration failures are printed by the CLI as plain messages with a non-zero exit status; no numbered diagnostic is emitted
E304	MISSING_RETURN is not enforced; the type checker reports E101 instead
W101	UNUSED_VARIABLE was documented but never emitted; removed rather than shipped as half-working
W102	UNUSED_IMPORT was documented but never emitted; removed rather than shipped as half-working